PASCal: a principal axis strain calculator for thermal expansion and compressibility determination

Abstract

This article describes a web‐based tool (PASCal; principal axis strain calculator; http://pascal.chem.ox.ac.uk) designed to simplify the determination of principal coefficients of thermal expansion and compressibilities from variable‐temperature and variable‐pressure lattice parameter data. In a series of three case studies, PASCal is used to reanalyse previously published lattice parameter data and show that additional scientific insight is obtainable in each case. First, the two‐dimensional metal–organic framework [Cu2(OH)(C8H3O7S)(H2O)]·2H2O is found to exhibit the strongest area negative thermal expansion (NTE) effect yet observed; second, the widely used explosive HMX exhibits much stronger mechanical anisotropy than had previously been anticipated, including uniaxial NTE driven by thermal changes in molecular conformation; and third, the high‐pressure form of the mineral malayaite is shown to exhibit a strong negative linear compressibility effect that arises from correlated tilting of SnO6 and SiO4 coordination polyhedra.

Direct visualization of a guest-triggered crystal deformation based on a flexible ultramicroporous framework

“…Solvent accessible voids were calculated using the SOLV routine of PLATON. Thermal expansion coefficients of the principal axes (a 0 , b 0 and c 0 ) were calculated using the PASCal program 50 .…”

Compositional dependence of anomalous thermal expansion in perovskite-like ABX3formates

“…56 For this particular structure, the projection from lattice parameter coordinates onto XBUs is given by the pair of equations r = 1 3…”

Uniaxial negative thermal expansion and metallophilicity in Cu3[Co(CN)6]

“…Coefficients of thermal expansion were determined using linear fits to the lattice parameter data [39], and are given in . We will come to rationalise the differences in behaviour of the copper(I) and silver(I) hexacyanocobaltates below, but include first some additional analysis of the trends in lattice parameters we observe using our newly-measured data.…”

“…We employed estimated temperature uncertainties of 5 K and fitted the principal axis expansivities using linear functions. For internal consistency with the uniaxial expansivities, the volume expansivity was determined using the trace of the expansivity tensor [40] rather than via the direct V-T fit given by PASCal [39].…”